Well first, it's important to point out that this is not a Wordpress site. It's a web application or SaaS. Perhaps it was built with Ruby, Python, or it could be using other JS frameworks/languages. There are many reason why you would not use WP for a site like this, one of those reasons is: Scale. WP sites do not scale well. I would start there. I would research building a web app vs. Wordpress. You will find much insight in regards to scale. This is a great article to introduce you to WP scale and what issues you may run into: https://tommcfarlin.com/scaling-wordpress/